Re: [Qemu-devel] [PATCH v3 4/6] spapr_pci: enumerate and add PCI device tree

[Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>]

Thomas Huth <thuth@redhat.com> writes:

> On Tue,  5 May 2015 14:23:54 +0530
> Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> wrote:
>
>> All the PCI enumeration and device node creation was off-loaded to
>> SLOF. With PCI hotplug support, code needed to be added to add device
>> node. This creates multiple copy of the code one in SLOF and other in
>> hotplug code. To unify this, the patch adds the pci device node
>> creation in Qemu. For backward compatibility, a flag
>> "qemu,phb-enumerated" is added to the phb, suggesting to SLOF to not
>> do device node creation.
>> 
>> Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
>> ---
>>  hw/ppc/spapr_pci.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++++++---
>>  1 file changed, 103 insertions(+), 5 deletions(-)
>> 
>> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
>> index 8b02a3e..103284a 100644
>> --- a/hw/ppc/spapr_pci.c
>> +++ b/hw/ppc/spapr_pci.c
>> @@ -23,6 +23,7 @@
>>   * THE SOFTWARE.
>>   */
>>  #include "hw/hw.h"
>> +#include "hw/sysbus.h"
>>  #include "hw/pci/pci.h"
>>  #include "hw/pci/msi.h"
>>  #include "hw/pci/msix.h"
>> @@ -35,6 +36,7 @@
>>  #include "qemu/error-report.h"
>>  #include "qapi/qmp/qerror.h"
>>  
>> +#include "hw/pci/pci_bridge.h"
>>  #include "hw/pci/pci_bus.h"
>>  #include "hw/ppc/spapr_drc.h"
>>  #include "sysemu/device_tree.h"
>> @@ -945,7 +947,10 @@ static int spapr_populate_pci_child_dt(PCIDevice *dev, void *fdt, int offset,
>>       * processed by OF beforehand
>>       */
>>      _FDT(fdt_setprop_string(fdt, offset, "name", "pci"));
>> -    _FDT(fdt_setprop(fdt, offset, "ibm,loc-code", drc_name, strlen(drc_name)));
>> +    if (drc_name) {
>> +        _FDT(fdt_setprop(fdt, offset, "ibm,loc-code", drc_name,
>> +                         strlen(drc_name)));
>> +    }
>>      _FDT(fdt_setprop_cell(fdt, offset, "ibm,my-drc-index", drc_index));
>>  
>>      _FDT(fdt_setprop_cell(fdt, offset, "#address-cells",
>> @@ -1001,10 +1006,6 @@ static void spapr_phb_add_pci_device(sPAPRDRConnector *drc,
>>      void *fdt = NULL;
>>      int fdt_start_offset = 0;
>>  
>> -    /* boot-time devices get their device tree node created by SLOF, but for
>> -     * hotplugged devices we need QEMU to generate it so the guest can fetch
>> -     * it via RTAS
>> -     */
>>      if (dev->hotplugged) {
>>          fdt = spapr_create_pci_child_dt(phb, pdev, drc_index, drc_name,
>>                                          &fdt_start_offset);
>> @@ -1482,6 +1483,89 @@ PCIHostState *spapr_create_phb(sPAPREnvironment *spapr, int index)
>>      return PCI_HOST_BRIDGE(dev);
>>  }
>>  
>> +typedef struct sPAPRFDT {
>> +    void *fdt;
>> +    int node_off;
>> +    uint32_t index;
>> +} sPAPRFDT;
>> +
>> +static void spapr_populate_pci_devices_dt(PCIBus *bus, PCIDevice *pdev,
>> +                                          void *opaque)
>> +{
>> +    PCIBus *sec_bus;
>> +    sPAPRFDT *p = opaque;
>> +    int ret, offset;
>> +    int slot = PCI_SLOT(pdev->devfn);
>> +    int func = PCI_FUNC(pdev->devfn);
>> +    char nodename[512];
>
> That's quite a big array ....
>
>> +    sPAPRFDT s_fdt;
>> +
>> +    if (func) {
>> +        sprintf(nodename, "pci@%d,%d", slot, func);
>> +    } else {
>> +        sprintf(nodename, "pci@%d", slot);
>> +    }
>
> ... just for holding such a small string. Could you maybe use
> a smaller array size for nodename (especially since you call this
> function recursively)?

Sure, will change this to 32 bytes, that should be sufficient. 

>
>> +    offset = fdt_add_subnode(p->fdt, p->node_off, nodename);
>> +    ret = spapr_populate_pci_child_dt(pdev, p->fdt, offset, p->index, 0, NULL);
>
> The above code sequence looks pretty much similar to
> spapr_create_pci_child_dt() ... maybe it's worth the effort to merge
> the common code of both functions into a separate helper function
> to avoid the duplication? ... not sure if this is worth the effort,
> it's just a suggestion.

I had thought about it earlier but something was not matching. Let me
have a relook, things have changed.

>
>> +    g_assert(!ret);
>
> You know that assert statements can simply be disabled by a
> preprocessor switch - and in that case there is no more error handling
> here at all and the code continues silently with a partial initialized
> node!

Thanks for bringing this to notice, assert() ?

> So it's maybe better to do a proper error handling here instead?

Will change this error handling here.

>
>> +    if ((pci_default_read_config(pdev, PCI_HEADER_TYPE, 1) !=
>> +         PCI_HEADER_TYPE_BRIDGE)) {
>> +        return;
>> +    }
>> +
>> +    sec_bus = pci_bridge_get_sec_bus(PCI_BRIDGE(pdev));
>> +    if (!sec_bus) {
>> +        return;
>> +    }
>> +
>> +    s_fdt.fdt = p->fdt;
>> +    s_fdt.node_off = offset;
>> +    s_fdt.index = p->index;
>> +    pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
>> +                        spapr_populate_pci_devices_dt,
>> +                        &s_fdt);
>> +}
>> +
>> +static void spapr_phb_pci_enumerate_bridge(PCIBus *bus, PCIDevice *pdev,
>> +                                           void *opaque)
>> +{
>> +    unsigned short *bus_no = (unsigned short *) opaque;
>
> opaque is a void pointer, so I think you don't need the typecast here.

Ok, QEMU has strong type checking, so by default I typecast them every time.

>
>> +    unsigned short primary = *bus_no;
>> +    unsigned short secondary;
>> +    unsigned short subordinate = 0xff;
>
> Is there a special reason for using unsigned short variables here?

No special reason, actually unsigned char should do, as the max is bus
number can only be 255

> "unsigned int" would sound much more natural to me.
>
>> +    if ((pci_default_read_config(pdev, PCI_HEADER_TYPE, 1) ==
>> +         PCI_HEADER_TYPE_BRIDGE)) {
>> +        PCIBus *sec_bus = pci_bridge_get_sec_bus(PCI_BRIDGE(pdev));
>> +        secondary = *bus_no + 1;
>> +        pci_default_write_config(pdev, PCI_PRIMARY_BUS, primary, 1);
>> +        pci_default_write_config(pdev, PCI_SECONDARY_BUS, secondary, 1);
>> +        pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, secondary, 1);
>> +        *bus_no = *bus_no + 1;
>> +        if (sec_bus) {
>> +            pci_default_write_config(pdev, PCI_PRIMARY_BUS, primary, 1);
>> +            pci_default_write_config(pdev, PCI_SECONDARY_BUS, secondary, 1);
>> +            pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, subordinate, 1);
>
> You write all value here again ... I think you c\ould either drop the
> write to the PRIMARY and SECONDARY BUS registers, or you could use a
> proper if-else instead.

I will drop the PRIMARY and SECONDARY here, that would do.

>
>> +            pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
>> +                                spapr_phb_pci_enumerate_bridge,
>> +                                bus_no);
>> +            pci_default_write_config(pdev, PCI_SUBORDINATE_BUS, *bus_no, 1);
>> +        }
>> +    }
>> +}
>> +
>> +static void spapr_phb_pci_enumerate(sPAPRPHBState *phb)
>> +{
>> +    PCIBus *bus = PCI_HOST_BRIDGE(phb)->bus;
>> +    unsigned short bus_no = 0;
>
> Again, why "short" ?
>
>> +    pci_for_each_device(bus, pci_bus_num(bus),
>> +                        spapr_phb_pci_enumerate_bridge,
>> +                        &bus_no);
>> +
>> +}
>> +
>>  int spapr_populate_pci_dt(sPAPRPHBState *phb,
>>                            uint32_t xics_phandle,
>>                            void *fdt)
>> @@ -1521,6 +1605,8 @@ int spapr_populate_pci_dt(sPAPRPHBState *phb,
>>          cpu_to_be32(b_ddddd(-1)|b_fff(0)), 0x0, 0x0, cpu_to_be32(-1)};
>>      uint32_t interrupt_map[PCI_SLOT_MAX * PCI_NUM_PINS][7];
>>      sPAPRTCETable *tcet;
>> +    PCIBus *bus = PCI_HOST_BRIDGE(phb)->bus;
>> +    sPAPRFDT s_fdt;
>>  
>>      /* Start populating the FDT */
>>      sprintf(nodename, "pci@%" PRIx64, phb->buid);
>> @@ -1570,6 +1656,18 @@ int spapr_populate_pci_dt(sPAPRPHBState *phb,
>>                   tcet->liobn, tcet->bus_offset,
>>                   tcet->nb_table << tcet->page_shift);
>>  
>> +    /* Walk the bridges and program the bus numbers*/
>> +    spapr_phb_pci_enumerate(phb);
>> +    _FDT(fdt_setprop_cell(fdt, bus_off, "qemu,phb-enumerated", 0x1));
>> +
>> +    /* Populate tree nodes with PCI devices attached */
>> +    s_fdt.fdt = fdt;
>> +    s_fdt.node_off = bus_off;
>> +    s_fdt.index = phb->index;
>> +    pci_for_each_device(bus, pci_bus_num(bus),
>> +                        spapr_populate_pci_devices_dt,
>> +                        &s_fdt);
>> +
>>      ret = spapr_drc_populate_dt(fdt, bus_off, OBJECT(phb),
>>                                  SPAPR_DR_CONNECTOR_TYPE_PCI);
>>      if (ret) {
>
>  Thomas

Regards
Nikunj